Minimizing or preventing the deposit of pitch in pulp and paper making processes is critical to minimizing equipment fouling and paper machine down time, maximizing production efficiency, and improving product quality. Pitch is composed of low molecular weight olephilic materials (primarily triglycerides, fatty acids, terpenes, resin acids and esters), which are released from wood fibers during chemical and mechanical pulping processes. These resinous substances usually precipitate as calcium and magnesium salts, causing problems with the wet end components of paper machines.
Known methods for pitch control include cationic fixation with cationic polymers, dispersion with surfactants, absorption with talc, and chelation with heavy metals. Enzymatic methods also are known. For example, U.S. Pat. No. 5,176,796 to Irie, et al, discloses adding acylglycerol lipase to mechanical pulp paperstock or reuse water. U.S. Pat. No. 5,256,252 to Sarkar et al. discloses adding a lipase and a cationic polymer to a papermaking cellulosic slurry. U.S. Pat. No. 5,667,634 to Fujita et al. discloses adding a water-soluble polyelectrolyte to increase the hydrolysis rate of esters in the presence of a lipase.
Effectively employing these and other pitch control methods, however, requires an accurate assessment of the quantity of depositable pitch present in the pulp and process waters throughout several points in the papermaking process. Standard diagnostic techniques for measuring pitch include a test to measure the total organic extractive content of the pulp. Unfortunately, known methods of total organic extractive content determinations, fatty acid analysis, or triglyceride analysis of pulp take between about 8 and 24 hours to complete. Therefore, the test results are useful only for post evaluation of the process system; they do not provide an assessment of the current state of the process, and yield unreliable and unfocused results. Accordingly, use of analytical methods to accurately apply pitch control measures is quite limited, as the dynamic nature of the pitch level in a continuous papermaking process requires a timely response with the pitch control strategies. It would be highly advantageous to have a method that analyzes the triglyceride and/or fatty acid content of the pulp quickly and accurately so that process parameters can be adjusted to timely and accurately prevent pitch deposition problems.
One current method of triglyceride analysis is based on the analysis of fatty acids produced by the hydrolytic reaction of triglyceride in the presence of lipase:

The method steps include (1) analyzing the fatty acid content of a first pulp sample that has not been treated with enzyme using an extraction, evaporation, and titration procedure; (2) calculating the percent of organic acid as oleic acid for the first sample; (3) treating a second pulp sample with a high dose of enzyme under conditions to ensure complete conversion of triglyceride to fatty acids and glycerol; (4) analyzing the fatty acid content of the enzyme-treated second pulp sample using the extraction, evaporation, and titration procedure; and (5) comparing the difference of organic acid in the first sample and the second sample. The triglyceride content is determined by the difference of fatty acid content before and after lipase treatment of the pulp sample, multiplied by a conversion factor. The conversion factor is the ratio of the molecular weight of the triglycerides to the molecular weight of the fatty acids. It is assumed that at high lipase dosage, the triglycerides are converted entirely to fatty acids and glycerol. No side reactions occur.
Various methods have been proposed for free fatty acid analysis. One method is that free fatty acid is first extracted with one or more organic solvents. The extensive extraction, evaporation, and titration by alkali procedures required to assess fatty acid content are time consuming and labor intensive. For example, the fatty acids in the pulp sample are extracted into a hexane layer and aliquots of the hexane layer then are evaporated, leaving an organic residue that subsequently is dissolved into an aqueous isopropanol solution, which is then titrated with potassium hydroxide solutions using thymol blue as a pH indicator. Due to the multiple steps involved, there exists the problem of poor reproducibility with this method as well as the time it takes to complete the procedure.
Another method for free fatty acid analysis also involves an extensive solvent extraction step followed by a high cost instrumental analysis step, involving high performance liquid chromatography (HPLC), thin layer chromatography (TLC), or gas chromatography (GC). These extraction-based methods typically take between about 8 and 24 hours to complete, require the use of potentially dangerous volatile organic compounds or toxic solvents, and are very labor intensive. The instrumental analysis is not portable for on site analysis, and the results often are inaccurate or irreproducible. It would be advantageous to have an accurate test method that does not require the extraction step, so that the pulp could be tested directly and rapidly. Such a test preferably would be portable, fast and easy to use, without high cost instrumental analysis. It would be beneficial if the method also minimized or eliminated the tester's potential exposure to volatile organic compounds or toxic solvents required by the extraction-based methods.
Pitch on the surface of the pulp fibers or in the suspension, i.e. the depositable pitch, is the greatest concern in pitch deposition in pulping and paper manufacturing mills. Total pitch consists of pitch located on the surface of the fibers and pitch trapped within the pulp fibers. The pitch trapped within the fibers generally does not contribute to the pitch deposition problem, as it remains intact within the fibers and does not have a chance to deposit. Therefore, a test method providing results that directly correlate to pitch depositions problems would be highly beneficial.
U.S. Pat. No. 7,067,244 “Rapid Triglyceride Assay for Use in Pulp Pitch Control” Jiang et al. describes enzymatic methods for determining the surface triglycerides content in a wood pulp sample. The methods comprise reacting triglycerides which are present on the surface of the wood or in the whitewater in the presence of a lipase to form glycerol and fatty acids, and then determining the difference between the amount of free glycerol present in the sample and the amount of glycerol formed from the triglycerides.
Gaining such an understanding of fatty acid concentration can be quite valuable since fatty acids can create much broader problems than triglycerides. Fatty acids are a component of the natural extractives of wood pulp. The concentration of free fatty acids in the pulp is a function of the species of trees used, the maturity of the tree, growing conditions, harvesting season, the debarking process, the storage of the wood and seasoning/aging of the wood, and, more important, the pulping method used in the pulp production. In mechanical pulping which uses little or no chemicals, only limited chemical changes occur to the wood extractives and their relative distribution. However, in chemical (kraft) pulping, the extractives are subjected to intensive chemical reactions, therefore both the chemical composition and relative distribution of wood extractives change substantially. For example, during the cooking stage with the pH near 14, wood extractives react with strong caustic chemicals. Therefore, glycerides are converted to fatty acids, and then the fatty acids are saponified to fatty soaps. In the bleaching stages, strongly oxidative chemicals, such as ClO2, H2O2, and O3, will then oxidize unsaturated fatty acids. Therefore, kraft pitch is fundamentally different from mechanical pitch.
Moreover, many treatments used in the pulping of recycled fiber, such as deinking, involve fatty-acid-based chemicals, either fatty acids or fatty soaps. Some of the chemicals will be carried over to the papermaking process. Naturally occurring fatty acids, fatty acids generated from the triglyceride conversion by lipase enzyme, and the carry over of fatty acid-based chemicals can cause problems with the wet end components of paper machines if they are not managed properly. At present, the management of fatty acids generated from enzyme conversion is difficult to do. This is chiefly due to the lack of an effective tool for quantitatively monitoring the generation, flow, distribution, and accumulation of fatty acids in the system.
Therefore, it would be desirable to provide methods, devices, and kits for accurately and rapidly determining the fatty acid content of a pulp sample, particularly for use in a continuous papermaking process. It would also be desirable to provide methods for enhancing the effectiveness of pitch control measures in a papermaking process based on such determinations. It would further be desirable to provide methods for measuring the surface and/or colloidal fatty acids in wood pulp, wherein the test is portable, fast and easy to use without high cost instrumental analysis, and minimizes or eliminates the tester's potential exposure to volatile organic compounds or toxic solvents required by extraction-based total organic content diagnostic assays.
Therefore, it is an object of the invention to provide methods, devices, and kits for accurately and rapidly determining the fatty acid content of a pulp sample, particularly for use in a continuous papermaking process.
It is further an object of the invention to provide methods for enhancing the effectiveness of pitch control measures in a papermaking process based on such determinations.
It is a further an object of the invention to provide methods for measuring the surface and/or colloidal fatty acid content in wood pulp, wherein the test is portable, fast and easy to use without high cost of instrumental analysis, and minimizes or eliminates the tester's potential exposure to volatile organic compounds or toxic solvents required by extraction-based total organic content diagnostic assays.